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The naturally occurring phytocidal chemical components of some Thai plant-species are responsible for controlling and repelling insects from the host plants. The aim of this study was to evaluate the insecticidal activity of Jatropha gossypifolia L. Leaf extracts and the senescent leaf Cleome viscosa L. (Capparidacae) against S. litura and detoxification enzyme activities. Laboratory no-choice bioassays showed treatment of second instars Spodoptera litura by dipping in extracts from senescent Leaves of Jatropha gossypifolia L. at 3000-10000 ppm had significant toxicity with LC50 of 6.56 mg/ml(-1) (r2=0.88) at 24 hours after exposure. The toxicity of Cleome viscosa L. extract in terms of LC50 values ca. 34 mg ml(-1) (r2=0.95) at 24 after exposure by the dipping method. ALso, S. litura Larvae surviving treatment of both extract showed a dramatic decrease in carboxylesterase and glutathione-s-transferase activities. This extract showed strong insecticidal activity and may play an alternative role as a pesticide against Spodoptera litura.

Jotropha gossypifolio L. (Etphorbiaceae) and Cleome viscosa, L. (Capparidacae), Thai-plant species, have phytocidal chemical components and responsible for controlling and repelling insects from the host plants. To avoid potential toxic pollutant contaminating aquatic ecosystems, this present study was investigated for acute toxicity. Guppy fish (Poecilia reticulata) were selected for the bioassay experiments. The experiments were repeated 5 times and the 24-h LC50 was determined for the guppies. The acute toxicity experiments were carried out by static method and behavioral changes in guppies were determined for each Jatropha gossypifolia L. and Cleome viscosa, L. concentration extract which extracted by Soxhlet extraction method with ethanol as solvent. Water temperature was regulated at 20 +/- 1 degrees C. Data obtained from the acute toxicity tests were evaluated using the probit analysis statistical method. The 24-h LC50 value for guppy was estimated as ca. 3100 ppm (r2=0.95) and 5300 ppm ((r2=0.96) for Jatropha gossypifolia L. and Cleome viscosa, L. extract, respectively. However, in this concentration, no mortality was observed at higher concentration for 30 second.

Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), an important insect pest of many field crops, has developed resistance to various insecticides, making its control increasingly difficult. This study explored the effects of senescent Leaf Melia azedarach L. (Meliaceae) and Amaranthus viridis L. (Amaranthaeae) extract on second instar S. exigua Larvae survival by the dipping method. We also analyzed detoxification enzyme activities of carboxylesterase and gLutathione-s-transferase in in vitro tests with extract-treated insects. The leaf extract showed strong insecticide activity with a LC50 value of 9.793 mg/ml (r2 = 0.965) and 50.5702 mg/mi (r2 = 0.95) at 24 after exposure for M. azedarach L. and A. viridis L. extract, respectivrly but no significant increase in toxicity over time. The M. azedarach L. extract strongly inhibited all enzyme activities. In contrast with A. viridis L. extract, they inhibit only glutathione-s-transferase. This is the first report of highly effective insecticidal activity of the senescent leaf extract of A. viridis and M. azedarach L. against S. exigua. Both plant materials are a less expensive (0.5 $US per 1 kg leaf), suggesting this extract is a promising alternative tool for the management of this pest.

The brown planthopper, Nilaparvato lugens Stat. (BPH) is the most devastating insect pest in rice fields. Outbreaks of BPH, which are resistant to many synthetic insecticides, can cause total rice crop loss. This research was done to evaluate the efficiency of extracts of mangosteen pericarp (Garcina mangostana L.) as an alternative control of BPH Thailand strain. Topical spraying was applied to various stages of nymphal and adult BPH to determine toxicity. An ethanol extract of mangosteen pericarp extract gave the best control of BPH, with LC50 of 4.5% w/v (r2 = 0.95) with 3rd instar BPH nymphs when compared with the other solvents, hexane, acetone and dichloromethane. The active compound, alpha-mangostin showed an LC50 of 5.44%w/v (r2 = 0.88). The toxicity of this extract was less than that of Imidacloprid which showed an LC50 of 0.0042% w/v (r2 = 0.99). The toxicity to non-target organisms was determined. This extract showed toxicity to guppies ((LC50 = 2.53 and 4.27 ppm for females and males, respectively; r2 = 0.97 and 0.97, respectively), bees (LC50 = 4.38% w/v, r2 = 0.95) and mice (no oral acute toxicity and no dermal inflammation but showed eye irritation in 1 day which became normal within 3 days). In vitro detoxification enzyme activities of carboxylesterase, acetylcholinesterase and glutathione-s-transferase from BPH after 24 hours exposure were also observed. Carboxylesterase showed stronger activity than other enzymes. Toxicity in terms of LC50 values of both the extract and imidacloprid treatments increased in each generation. The LC50 values for each generation were 4.22-6.67 after sequential spraying. After the ethanol extract was kept at 4 degrees C, room temperature and 55 degrees C for 3 months, the quantity of alpha-mangostin and the BPH control efficiency was lower at 55 degrees C than those for other temperatures. The results from this research indicate that mangosteen pericarp extract can be an alternative insecticide for the control of BPH, which may possess high efficiency, cause with fewer environmental problems and result in less resistance in the BPH.